1. Field of the Invention
The present invention relates to paper folding devices having a function of being capable of folding paper a plurality of times, finishers provided with this paper folding device, and image forming apparatuses such as copying machines, printers, facsimile machines, or digital multifunction devices, provided with this paper folding device or finisher.
2. Description of the Background Art
Paper folding devices such as those disclosed in Japanese Patent Application Laid-open No. 2004-67266 (hereinafter referred to as Prior Art 1) and Japanese Patent No. 3,356,851 (hereinafter referred to as Prior Art 2) are known as examples of devices that have two pairs of folding rollers that bend paper, a pair of carry rollers that feed paper to either of the roller pairs, and a biasing means that switches a direction in which the paper bends to either of the folding rollers, and are capable of alternately switching the bending direction to fold paper continuously a plurality of times. These devices have biasing means that push a central portion of the paper toward a rolling position at a nip of the folding rollers.
However, as is described later, in these conventional paper folding devices, there is large unevenness in folding positions due to thick papers and thin papers, and unevenness in the folding positions for single folds and multiple folds, and therefore there have been problems of having low folding accuracy and unstable folding functions.